In my previous post, I discussed basic terminology we use in the field of lower extremity biomechanics. Now, to continue this discussion, I will present more terminology used in the daily practice of diagnosing and treating conditions with custom foot orthotic devices. Basic knowledge of foot and ankle anatomy is assumed, as well as normal physiology (function of the anatomy), pathology or deviation from the normal functionality, as well as treatment of the pathology in order to restore normal physiology as much as possible. Our ability to walk upright on two limbs is miraculous, yet imperfect, and infinitely complicated, so breaking things down to basics is always a good idea to see pathology clearly and have understanding what treatment objectives should be for all our patients.
Body planes regarding the foot
Sagittal (Longitudinal) Plane - vertical plane, divides body into left and right halves
Frontal (Coronal) Plane- vertical plane, divides body into front and back halves
Transverse (Axial) Plane- horizontal plane, divides body into top and bottom halves
Foot position and direction of motion
Inversion - motion towards from the midline of the body, generally on the frontal plane
Eversion - motion away from the midline of the body, generally on the frontal plane
Varus - Inverted position of a body part, laterally tilted
Valgus - Everted position of a body part, medially tilted
Adduction - Motion towards the midline of the body on the transverse plane
Abduction - Motion occurring away from the midline of the body on the transverse plane
Dorsiflexion - Motion occurring upwards on the sagittal plane
Plantarflexion - Motion occurring downwards on the sagittal plane
Supination - Motion occurring in the triplane direction of inversion, adduction and plantarflexion
Pronation - Motion occurring in the triplane direction of eversion, abduction, and dorsiflexion
Much confusion and misunderstanding occurs with the terminology of "pronation" and “supination” of the feet. Both terms reference both a position as well as a direction of motion. In other words, a foot may be in a pronated position, yet supinating in direction and vice versa. This is analogous to being on the east side of town, yet heading in a westerly direction. When we discuss “pronation" and “supination” we are generally discussing motion of the Subtalar Joint (Talo-Calcaneal Joint) and the Midtarsal Joint (Talo-Navicular Joint and Calcaneal-Cuboid Joint) which largely work in conjunction with each other. When the foot pronates, it tends to become flatter, more flexible and adaptive, when the foot supinates, it tends to be higher arched, rigid and supportive.
Pronation and supination, as discussed above, are tri-planar motions which are largely rotational in nature. Rotation occurs about an axis of motion, which is perpendicular to the direction of the motion, such as the wheels rotating perpendicular to the axles on an automobile.
In the foot, we discuss the concept of “planar dominance” in regards to the subtalar axis affecting pronation and supination. Some people have a more horizontal oriented axis which will lead to proportionally more inversion-eversion versus abduction-adduction. Others, might have a more vertically oriented axis, which will create more proportionally abducted-adducted motion than inversion and eversion. In other words, some people will roll in and out more than they turn in and out, and vice versa. Sometimes this will be obvious in more limber people than less limber people, sometimes it will be quite subtle. Additionally, there is a 4th dimension to this, and that is timing. A foot may be overpronated at certain points of the gait cycle and oversupinated at other points of the gait cycle. It can be very complicated and confusing!
More often than not, we utilize custom foot orthoses to alleviate conditions related to over-pronation of the foot. Mostly the overpronation is a response to compensate for a structural or functional deficiency, which can be measured. The orthosis alters the weight bearing surface the foot interacts with, and therefore mitigates the need for the foot to compensate. For example, if a person has a natural varus or supination of the forefoot relative to the rearfoot, they will tend to pronate (evert, dorsiflex and abduct) to compensate for it. A correction for this is built into the orthotic device in the form of a forefoot post, thus allowing the foot to perform its primary function of forward propulsion in a more efficient manner, without the need to compensate for a deformity. It’s science, but works like magic!
